The Waterwitch is chiefly remarkable for the trial given in her to Mr. Ruthven’s system of hydraulic propulsion. A small boat was fitted with the machinery and tried on the Thames. A vessel provided with the Ruthven apparatus was built to the order of the Prussian Government in 1853, and for many years worked satisfactorily on the Oder. The chief engineer of Portsmouth Dockyard, when testifying to the Government as to the capabilities of the Ruthven method, said it afforded extraordinary facilities for manœuvring under steam, and he saw no reason why a speed should not be attained with it equal to that of the paddle or screw. A vessel called the Seraing was built by the Belgian shipbuilding firm of Cockerill and fitted with a Ruthven propeller, and when tried against a paddle-wheel vessel of the same form, tonnage, and horse-power was found to have about 10 per cent. greater speed than the other. The testimony of the chief engineer of the Portsmouth Dockyard resulted in the Waterwitch experiment. The hull of this vessel was constructed by the Thames Iron Works and Shipbuilding Company, and the design of the engines and the construction of the enormous turbine wheel, of which the propeller consists, were entrusted by the Admiralty to Messrs. Dudgeon. The Waterwitch was built of iron and was of 778 tons measurement, 162 feet in length by 32 feet in breadth, and 13 feet 9 inches in depth. She was flat-bottomed, broad in proportion to her length, and double-ended and had a rudder at each end. Her armour consisted of a belt of plating 4¹⁄₂ inches in thickness at the water-line and centrally on her broadside, with armour-plated bulkheads across her upper deck, the object of the latter arrangement being to enable her to fight her guns over her deck in line with her keel, through gunports in the thwartship bulkheads as well as through broadside ports. For the machinery, and in the bottom of the vessel near the centre, was a long and shallow iron box with its length in the direction of the vessel. The lower side of this box had an immense number of small rectangular orifices, admitting water from outside and under the ship’s bottom, the passage of the water being controlled by valves which were only opened when the engines were at work. The turbine wheel drew the water in through the bottom of the vessel and ejected it through copper propulsion pipes and nozzles, through an aperture on each side of the ship, a little below the water-line.
The propelling power of the hydraulic wheel is obtained from the force and volume of the column of water ejected by the wheel from the discharge pipes, on a principle that a gun recoils on being discharged, but with this difference, that the recoil from the water-wheel is continuous. If the column of water were discharged towards the stern the vessel moved forward, and if towards the stem it moved in the other direction; if discharged in both directions the vessel remained stationary, and if discharged forward on one side and towards the stern on the other, the vessel turned either on her centre as on a pivot, or if the pressure were greater in one direction than in the other, in a circle the size of which depended on the pressure of the discharge from either set of nozzles. No reversing of the engines or of the hydraulic wheel was required under any circumstances, the direction and force of the discharge being regulated by a series of valves. The hydraulic wheel was fixed immediately over the sluice valves and water-box, and revolved in a cast-iron circular case 19 feet in diameter. The wheel was itself 14 feet 6 inches in diameter and weighed eight tons, and was fitted with eleven vertical or radial arms and blades. The engines were of 160 nominal horse-power, and steam was supplied by two ordinary tubular boilers. At her trial the Waterwitch covered the measured mile in Long Reach in 6 minutes 20 seconds. At other trials later in the day she averaged 9 knots.
The shape of the vessel and the fact that she could be steered in either direction with equal facility were of undoubted advantage from the point of view of manœuvring, but the trials can hardly be called successful so much as experimental, as it was ascertained that she would probably have done better had her nozzles been differently placed and provision made for altering the size of the nozzles according to the speed at which the vessel was required to travel. The machinery itself, however, worked beautifully.
The Government ordered a number of comparative tests to be made in which the efficacy of the Waterwitch method could be judged against that of the double-screw system installed in the gunboats Viper and Vixen, all three vessels being of the same size. The two gunboats were not the best of their kind as they had double sternposts with a cavernous recess between them and flat overhanging sterns.
Mr. M. W. Ruthven, son of the inventor of the system, it being under his father’s patent that the Waterwitch machine was built, in addressing the Institute of Marine Engineers a few years ago, said:
“My efforts to make a ship safe, from an engineer’s point of view, lie in the method of propulsion. My plans are to apply all the engine-power of the ship to pumps for propulsion, and which can be used for pumping out leakage and propelling at the same time. In the largest pump I have made, 800 indicated horse-power discharged 350 tons of water a minute, and propelled the vessel faster than her sister ships with twin screws. The hydraulic propeller is of greatest value for the highest speeds, and has the greatest power of control. As the hydraulic is capable of subdivision to a great degree, the greatest amount of safety is possible. After an experience of sixty years of hydraulic propulsion, I am still of opinion that it is the means by which greater safety can be obtained at sea, and by which the highest speeds can be obtained with safety and economy.”[97]
[97] Institute of Marine Engineers’ Transactions, vol. ix.
This, however, was said before such phenomenal speeds were obtained with turbines and combined turbine and reciprocating engines.
A number of lifeboats fitted with jet-propelling machinery have been built by, among others, Messrs. Thornycroft, and have given every satisfaction. Whatever be the advantages of the system, and they are many, the drawbacks are very great, and the hydraulic method has been generally condemned because of the friction engendered by the pumping of such large quantities of water, and the probability of the inlet orifices becoming choked by sand, mud, or floating matter.
Notwithstanding its evident advantages, the screw propeller, whether single or double, had many enemies. It was asserted to be the cause of premature decay in both wood and iron vessels, and stringent orders were even given to ship captains to use canvas except in extreme cases when steam was absolutely necessary. “Our screw navy is, therefore,” said a paper of that period, “more of a sailing than a steam navy.” The twin-screw arranged by Messrs. Dudgeon was claimed to have developed the principle in such a way as to leave no doubt of its superiority over the single propeller. Twin-screws were no new thing at this time. Captain Smith, known as “Target Smith” because of his movable target in use on the Excellent, had experimented with some with a considerable measure of success, but it was Messrs. Dudgeon who solved the problem of twin-screw propellers for ocean-going steamers. They demonstrated that as good results could be got from two small propellers as from one large one.